Meiksin's research has concentrated largely on aspects of extra-galactic
astronomy and cosmology. His principal interests are the structure of the
Intergalactic Medium (the baryons left over from the Big Bang that didn't
make galaxies) and the Large-Scale Structure of the Universe. He is also a
Participant of the Sloan Digital Sky Survey , and maintains a
keen interest in the science that may be achieved with LOFAR and an envisioned Square Kilometre Array .

The Intergalactic Medium

Observations of intervening absorption lines in quasar spectra at redshifts
up to z = 6 provide invaluable insight into the primordial density fluctuation
spectrum and the chemical composition of some of the earliest formed
cosmological structures, as well as of the UV background that ionizes them.
Both the Lyman-α forest and the metal absorption systems are sensitive
probes of the epochs of galaxy formation, reionization, reheating, and the
chemical enrichment of the universe. Meiksin and his collaborators have
used numerical simulations of the formation of structure in the IGM to
study the properties of the Lyman-α forest predicted in Cold Dark Matter
dominated cosmologies. The simulations show that the structures giving rise
to the Lyman-α forest span a wide range in morphologies, from sponge-like
to sheet-like to filamentary to spheroidal. Virtually all the baryons in the
Universe are found to be contained in these structures at high redshifts.

21-cm Tomography

Measurements of the spectral and spatial structures of the 21-cm line
emission and absorption from HI at high redshifts may provide a means
of probing the epoch of heating of the IGM at 5 < z < 10 and its nature.
With his collaborators, Meiksin has shown how, through a combination
of preheating and radiation, an early generation of sources could excite
21-cm radiation from a warm HI component of the IGM prior to its complete
reionization. The resulting patchwork of 21-cm emission could serve as a
valuable tool for understanding the epoch, nature, and sources of the
reionization of the universe, as well as the morphology of the IGM at early
times. The patchwork may be detectable using the Low Frequency Radio
Array ( LOFAR ) in the Netherlands, or by a Square Kilometre Array
( SKA ).

The Large-Scale Structure of the Universe

Our understanding of the formation of galaxies and their clustering has
developed enormously in the past 2 decades. The picture that has evolved
is that structures arise from the gravitational instability of initially small
density perturbations in an otherwise homogeneous expanding universe. The
Cold Dark Matter model has been the most successful in predicting the observed
properties and clustering patterns of galaxies. An essential tool in
establishing the connection between the initial density perturbations and
the clustering pattern of galaxies measured today is the power spectrum of
the density fluctuations. Meiksin and his collaborators have shown that
gravitational growth will induce correlations in the power spectrum between
different modes, which must be accounted for in making any statistical
comparison between the clustering of the galaxies and model predictions. They
have also shown that current large redshift surveys like the 2dF and the Sloan
Digital Sky Survey may
be able to detect a component in the power spectrum due to acoustic
oscillations of the baryons at the time of matter-radiation decoupling in the
early universe.

For publications and to learn more about the Sloan Digital Sky Survey, click
here